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<meta name="description" content="面向对象的第二大特点就是继承：而继承的主要作用在于在已有的基础上继续进行功能的扩充。 继承问题的引出如果想要更好的解释继承的作用，下面按照我们所学习到的概念来定义两个类：人，学生类。那么现在定义效果如下： Person类 123456789101112131415161718class Person&amp;#123;    private String name;    private int age;">
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<meta property="og:description" content="面向对象的第二大特点就是继承：而继承的主要作用在于在已有的基础上继续进行功能的扩充。 继承问题的引出如果想要更好的解释继承的作用，下面按照我们所学习到的概念来定义两个类：人，学生类。那么现在定义效果如下： Person类 123456789101112131415161718class Person&amp;#123;    private String name;    private int age;">
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        <p>面向对象的第二大特点就是继承：而继承的主要作用在于在已有的基础上继续进行功能的扩充。</p>
<h1 id="继承问题的引出"><a href="#继承问题的引出" class="headerlink" title="继承问题的引出"></a>继承问题的引出</h1><p>如果想要更好的解释继承的作用，下面按照我们所学习到的概念来定义两个类：人，学生类。那么现在定义效果如下：</p>
<p>Person类</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>Student类</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="keyword">private</span> String school;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setSchool</span><span class="params">(String school)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.school = school;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getSchool</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> school;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>可以看到两个类有大量的重复代码，以上的程序开发模式就是我们之前所采用的模式，单独的简单Java类，我们通过不断的编写可以发现程序之中会出现大量的重复代码。</p>
<p>虽然说在代码上重复了，但是又可以发现概念上来讲，一个学生一定是人，但是学生和人学生更加具体。学生描述的范围更小，具备的属性更多，方法也会更多，所以学生应该是人的一个扩充。</p>
<p>这个时候要想消除结构定义上的重复，就必须用继承来完成。</p>
<h1 id="继承的实现"><a href="#继承的实现" class="headerlink" title="继承的实现"></a>继承的实现</h1><p>在Java中使用我们的extends关键字来进行实现，其定义的语法如下：</p>
<ul>
<li><p>继承关系：<code>class 子类 extends 父类;</code></p>
<p> 子类在一些书上也被称为派生类，父类也被称为超类(SuperClass)。</p>
</li>
</ul>
<p>范例：继承的基本实现</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 继承;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line"></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">         Student stu = <span class="keyword">new</span> Student();</span><br><span class="line">         stu.setName(<span class="string">"kai"</span>);</span><br><span class="line">         stu.setAge(<span class="number">6</span>);</span><br><span class="line">         System.out.println(stu.getName()+<span class="string">"、"</span>+stu.getAge());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>通过此时的代码可以发现，当发生类继承关系之后，子类可以直接继承父类的操作，也就是说可以实现代码的重用。</p>
<p>子类最低也维持和父类相同的功能。当然子类也是可以进行扩充，例如：扩充属性和方法。</p>
<p>范例：子类进行功能的扩充。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 继承;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String school;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setSchool</span><span class="params">(String school)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.school = school;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getSchool</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> school;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">         Student stu = <span class="keyword">new</span> Student();</span><br><span class="line">         stu.setName(<span class="string">"kai"</span>);</span><br><span class="line">         stu.setAge(<span class="number">6</span>);</span><br><span class="line">         stu.setSchool(<span class="string">"利津一中"</span>);</span><br><span class="line">         System.out.println(stu.getName()+<span class="string">"、"</span>+stu.getAge()+<span class="string">"、"</span>+stu.getSchool());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>实现之后就可以非常清楚的发现，父类的确是可以进行功能的扩充，最重要的就是可以重用父类中定义的方法。</p>
<h1 id="继承的限制"><a href="#继承的限制" class="headerlink" title="继承的限制"></a>继承的限制</h1><p>虽然本质上来讲继承子类可以对父类操作进行共享，但是从另外一个角度来说，继承本生也是存在有一些限制的。</p>
<h2 id="子类对象在进行实例化之前一定会首先实例化父类对象，默认调用父类的构造方法之后再调用子类的构造方法进行子类的对象实例化。"><a href="#子类对象在进行实例化之前一定会首先实例化父类对象，默认调用父类的构造方法之后再调用子类的构造方法进行子类的对象实例化。" class="headerlink" title="子类对象在进行实例化之前一定会首先实例化父类对象，默认调用父类的构造方法之后再调用子类的构造方法进行子类的对象实例化。"></a>子类对象在进行实例化之前一定会首先实例化父类对象，默认调用父类的构造方法之后再调用子类的构造方法进行子类的对象实例化。</h2><p>必须先有老子，再有后代：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">    System.out.println(<span class="string">"Person类创建"</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="title">Student</span><span class="params">()</span></span>&#123;</span><br><span class="line">    System.out.println(<span class="string">"Student类创建"</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">    <span class="keyword">new</span> Student();</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>发现没有任何一条语句会明确的调用父类构造，但是父类的构造既然被执行了，所以就证明子类对象的实例化一定会实例化父类对象。但是需要注意的是，实际上这个时候在子类的构造方法之中相当于隐含了一个语句，这个语句<code>super()</code>。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">    System.out.println(<span class="string">"Person类创建"</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="title">Student</span><span class="params">()</span></span>&#123;</span><br><span class="line">    <span class="comment">//既然要进行构造方法的调用，那么构造方法的调用一定要写在首行。</span></span><br><span class="line">    <span class="keyword">super</span>();   <span class="comment">//此语句在无参是写与不写都一样</span></span><br><span class="line">    System.out.println(<span class="string">"Student类创建"</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span></span>&#123;</span><br><span class="line">  <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">    <span class="keyword">new</span> Student();</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>但是同时需要注意的是，如果此时你的父类里面没有提供有无参构造，这个时候就必须使用<code>super()</code>明确的指明你要调用的父类构造方法。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 继承;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">(String name,<span class="keyword">int</span> age)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String school;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Student</span><span class="params">(String name,<span class="keyword">int</span> age,String school)</span></span>&#123;</span><br><span class="line">        <span class="keyword">super</span>(name,age);</span><br><span class="line">        <span class="keyword">this</span>.school = school;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setSchool</span><span class="params">(String school)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.school = school;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getSchool</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> school;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">         Student stu = <span class="keyword">new</span> Student(<span class="string">"kai"</span>,<span class="number">18</span>,<span class="string">"利津一中"</span>);</span><br><span class="line">         System.out.println(stu.getName()+<span class="string">"、"</span>+stu.getAge()+<span class="string">"、"</span>+stu.getSchool());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h2 id="Java中只允许单继承不允许多继承"><a href="#Java中只允许单继承不允许多继承" class="headerlink" title="Java中只允许单继承不允许多继承"></a>Java中只允许单继承不允许多继承</h2><p>一个子类只能够继承一个父类。</p>
<p>范例：错误的多继承</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">A</span></span>&#123;&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">B</span></span>&#123;&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">C</span> <span class="keyword">extends</span> <span class="title">A</span>,<span class="title">B</span></span>&#123;&#125;</span><br></pre></td></tr></table></figure>
<p>实际上这个时候C类要同时继承A类和B类的主要目的是为了同时拥有A和B类中的操作，所以为了实现这样的概念可以同时采用多层继承的形式完成。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">A</span></span>&#123;&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">B</span> <span class="keyword">extends</span> <span class="title">A</span></span>&#123;&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">C</span> <span class="keyword">extends</span> <span class="title">B</span></span>&#123;&#125;</span><br></pre></td></tr></table></figure>
<p>但是这个层不建议太多了。一般我们自己在建立类的时候，这些类的继承关系也就最多3层结构了。</p>
<blockquote>
<p>总结Java不允许多重继承，但是允许多层继承。</p>
</blockquote>
<h1 id="在继承的时候，子类会继承父类的所有结构"><a href="#在继承的时候，子类会继承父类的所有结构" class="headerlink" title="在继承的时候，子类会继承父类的所有结构"></a>在继承的时候，子类会继承父类的所有结构</h1><p>但是这个时候需要注意的是，所有非私有操作属于显示继承（可以直接调用），而所有的私有操作属于隐式继承（通过其他形式调用例如：<code>setter getter</code>）。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 继承;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">this</span>.name;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span> <span class="keyword">extends</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">fun</span><span class="params">()</span></span>&#123;</span><br><span class="line">      System.out.println(getName());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">      Student stu = <span class="keyword">new</span> Student();</span><br><span class="line">      stu.setName(<span class="string">"张三"</span>);</span><br><span class="line">      System.out.println(stu.getName);</span><br><span class="line">      stu.fun();  </span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>此时父类中的属性的确被父类所继承了，但是发现子类能够使用的只是所有的非private操作（public），而所有的private操作肯定无法直接使用，所以称之为隐式继承。</p>
<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><ol>
<li>继承的语法以及继承的目的（扩展已有的类功能，是代码能够重用）；</li>
<li>子类的实例化流程：不管如何操作，一定要先实例化父类对象，而后再实例化子类对象；</li>
<li>继承的限制：不允许多重继承，只允许多层继承；</li>
</ol>

      
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